Semiconductor devices such as quantum cascade devices, interband cascade devices, and light-emitting diodes can be turned into tunable lasers through a variety of means. For example, a tunable laser can be an external cavity laser that includes the semiconductor device, and a tunable frequency selective element that is spaced apart from the semiconductor device. In this design, the semiconductor device is the laser gain medium, and the tunable frequency selective element is selectively tuned to adjust the center optical wavelength of an illumination beam generated by the tunable laser.
These external cavity lasers are often used in applications where it is desired to provide an illumination beam having a center optical wavelength that is varied over time over a tunable range, and then record the response of some sample as a function of the changing optical wavelength of the illumination beam. In such applications it is also often desired to tune the laser wavelength in a single sweep across the tunable range relatively quickly. This minimizes variations in the sample during data acquisition.
Unfortunately, existing semiconductor devices are not entirely satisfactory.